In a conventional digital full color copying machine, toner designing and setting of fixing conditions are made primarily in pursuit of color image formation as described in JP-A-2-293867 and JP-A-3-2765 (the term "JP-A" as used herein means an "unexamined published Japanese patent application"). Therefore, when the copying machine is applied to a black-and-white (hereinafter abbreviated as B/W) original, a black toner is excessively fused only to provide a B/W image rich in gloss as in the case of a full color mode.
Since a B/W image is generally desired to have low surface gloss, i.e., so-called matt finish, it has been difficult to broaden the market for a digital full color copying machine in offices where copying machines are used exclusively for copying of B/W images. Accordingly, there has been a keen demand for development of a digital full color copying machine with which matt B/W images are obtained.
It is known that gloss of a fixed image may be reduced by controlling molecular weight distribution of the polymer used in a toner to thereby control the viscoelasticity of the toner. However, mere control of the viscoelasticity of the toner as has been adopted in conventional electrophotographic techniques fails to obtain full color images rich in gloss. Besides, fusion of such a toner with controlled viscoelasticity is insufficient, causing a reduction in color developability and a reduction in light transmission of the resulting image formed on an OHP sheet.